Directed fabrication of radially stacked multifunctional oxide heterostructures using soft electron-beam lithography.

A versatile patterning approach based on electron-beam lithography (eBL) and solution deposition, termed soft-eBL, has been developed to fabricate radially stacked heterostructures of multifunctional oxides from their sol precursors. Well-defined nanorings of lead zirconate titanate (PZT) are fabricated on a variety of substrates such as noble metals (e.g., Au), semiconductors (e.g., Si), and oxide single crystals (e.g., SrTiO3), which were previously functionalized with appropriate self-assembled monolayers (SAMs). The undercut in the double-layer eBL resist and substrate functionalization with the SAM treatment play a vital role in the formation of the ring structures. The nanorings are then used as building block "containers" and ring-reservoirs are filled with a second sol (e.g., CoFe2O4) to form radially stacked composite ceramic heterostructures. The approach presented here does not require either feature alignment to realize heterostructures or the etching of ceramics, and is amenable to a variety of radially stacked composite heterostructures.

Effect of spatial confinement on the glass-transition temperature of patterned polymer nanostructures.

Poly(methyl methacrylate) (PMMA) nanostructures embedded with a fluorescence tag are fabricated using electron beam lithography on oxidized silicon substrates. The glass transition temperatures (Tgs) of these one-dimensional (1-D) nanostructures (parallel lines) are measured by monitoring their temperature-dependent fluorescence intensities, revealing substantial differences between the Tgs of the nanostructures and the thin films from which they were fabricated. For example, the Tg of 50-nm-wide PMMA nanolines on silica is approximately 15 K lower than that of a PMMA film on silica of the same 18 nm thickness. Attractive PMMA-silica interfacial interactions increase the Tg, while free surfaces decrease the Tg of PMMA in ultrathin films relative to bulk PMMA. Thus, the significant differences between the Tgs of the 1-D and two-dimensional (2-D) forms of PMMA on silica are the result of a substantial increase in the ratio of free-surface area to interfacial area in the PMMA nanolines relative to ultrathin films.